1. Field of the Invention
The present invention relates to an electrically conductive paste for forming an electrode or a circuit on a substrate such as a glass substrate, and more particularly, to an electrically conductive paste which is applied and baked to form an electrode to which an object is soldered by use of a solder containing no lead (hereinafter referred to as "lead-free solder"). The invention also relates to a glass substrate having a circuit thereon suitable for producing, for example, an automobile window having an antifogging property.
2. Background Art
Conventionally, an Sn/Pb eutectic solder has been widely used for soldering a conductor such as a lead terminal to a thick film electrode which is formed by applying and baking an electrically conductive paste.
In recent years, concern about the environment has increased, and material containing no toxic lead, i.e., a lead-free solder, has been gradually replacing a conventionally employed solder for connecting a lead terminal. Typically, there is widely employed a lead-free solder comprising Sn as a primary component and at least one metal selected from a group consisting of Bi, Ag, Zn, In and Sb.
However, when electric connection of a conductor such as a lead terminal is to be established by use of a lead-free solder, heat resistance and wettability of the conductor with respect to a solder are insufficient, resulting in poor reliability in terms of electric connection. This problem is partly due to the presence of a lead borosilicate glass frit contained in an electrically conductive paste which is used so as to enable the paste to be fired at a low temperature that allows use of a glass substrate.
In addition, regarding the glass frit that constitutes an electrically conductive paste, the glass frit itself, like a solder, is desirably employed as a lead-free material, in consideration of the environment.